Simple plugin system
extensions is a simple plugin system inspired from setuptools entry points
. It allows an application to define and/or use plugins.
A plugin can be any callable object . It has to be registered through the
For example, let’s take a simple function that calculates the average of
some numbers, and let’s save it into a file called
extensions.py in a
def average(*args): return sum(args) / len(args)
This function can be registered in the plugin system using the
function. Plugins have a name and belong to a group. For our
example, the group can be
myapp.operator and the name
from extensions import register # usage : register(group, name, location) register('myapp.operator', 'average', 'myapp.extensions:average')
The third parameter gives the location of the callable, with the form
module_name is the full name of the module,
attrs the attributes in the module.
Notice that the group name includes the name of the package, which is a good
practice to avoid collisions since the group names are global to all applications
There’s another way to register your plugins by using a configuration file.
You can write a ini-like file, using groups for sections title, and
name = location
for the values.
For example, if you create a
operators.cfg file with this content:
[myapp.operator] average = myapp.extensions:average
You will be able to load it using register_file:
from extensions import register_file register_file('operators.cfg')
This function will scan your file and register the plugins for you.
extensions provides a
get function that allows you to iterate over all
registered plugins for a given group:
from extensions import get for plugin in get(group='myapp.operator'): print plugin.name
You can also give the
name to the function:
for plugin in get(group='myapp.operator', name='average'): print plugin.name
Or even iterate over all plugins:
from itertools import islice for plugin in islice(get(), 5): print plugin.name
The objects returned by the
get function are
Plugin class instances.
Plugin class provides one method called
load, that returns
the registered object, so you can use it
# let's get the plugin `average` of the group `myapp.operator` plugin = get(group='myapp.operator', name='average').next() # let's load it func = plugin.load() # let's use it now average = func(1, 2, 3)
Plugin also provides a
name and a
group attribute, that corresponds
name of the registered plugin, and to its
If you want to distribute your plugins, you just have to import the module
that registers the plugins into your
from distutils.core import setup from myapp import plugins # registers the plugins setup(name='myapp', version='1.0' packages=['myapp'])
This will register the plugins when the package is installed by creating
a special file called
PLUGINS into the
.egg-info directory created when
your package is installed.
extensions is fully compatible with setuptools entry points. So you can iterate
and use entry points defined in third-party applications that are installed
in your Python.
If you want to iterate through setuptools entry points, use the
consume_entry_points option when you call the
plugins = get(consume_entry_points=True)
This will iterate over
extensions plugins and setuptools entry points.